The use of cellular communication systems having mobile devices which communicate with a hardwired network, such as a local area network (LAN) or a wide area network (WAN), has become widespread. Retail stores and warehouses, for example, may use cellular communications systems with mobile data terminals to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. Such systems are also utilized for cellular telephone communications to allow users with wireless telephones to roam across large geographical regions while retaining telephonic access. Paging networks also may utilize cellular communications systems which enable a user carrying a pocket sized pager to be paged anywhere within a geographic region.
A typical cellular communications system includes a number of fixed access points (also known as base stations) interconnected by a cable medium often referred to as a system backbone. Also included in many cellular communications systems are intermediate access points which are not directly connected to the system backbone but otherwise perform many of the same functions as the fixed access points. Intermediate access points, often referred to as wireless access points or base stations, increase the area within which access points connected to the system backbone can communicate with mobile devices.
Associated with each access point is a geographic cell. The cell is a geographic area in which an access point has sufficient signal strength to transmit data and receive data from a mobile device such as a data terminal or telephone with an acceptable error rate. Typically, access points will be positioned along the backbones such that the combined cell area coverage from each access point provides full coverage of a building or site.
Mobile devices such as telephones, pagers, personal digital assistants (PDA's), data terminals etc. are designed to be carried throughout the system from cell to cell. Each mobile device is capable of communicating with the system backbone via wireless communication between the mobile device and an access point to which the mobile device is registered. As the mobile device roams from one cell to another, the mobile device will typically deregister with the access point of the previous cell and register with the access point associated with the new cell. In order to provide sufficient cell area coverage, access points (or the antennas associated with each access point) within the cellular communications system typically are distributed at separate physical locations throughout an entire building or set of buildings.
Recently a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been adopted and has gained acceptance among the industrial, scientific and medical communities. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems. Current wireless implementations employ a single power level for transmission of an entire packet. As a result, different portions of the packet are capable of reception at different ranges. Therefore, default operation results in a longer preamble range as compared to the other portions of the frame. Once a preamble is correctly received by other access stations, they often need to remain off during an entire frame or frame exchange. This causes stations that are outside an intended transmission range to remain idle during the frame transmission thereby reducing the entire throughput of the system.
An attempt has been made to solve this problem by providing multiple access stations at a single location operating on different frequencies. However, this requires that each station in a single location be different with respect to hardware and software required to operate the station. This has proven to be complicated and expensive in actual implementation. In addition, there is typically only three non-overlapping channels available in such types of systems. Therefore, this solution does not overcome the problem with idle access stations when all three channels are operating. Furthermore, these transmissions along the three channels still do not guarantee access points will not receive interference.
Accordingly, there is a strong need in the art for a system and method that overcomes the aforementioned problems.